A handy graphic that shows what forms of light the human eye can readily see (Image Credit: Sara Dickherber)

The human eye is an amazing thing indeed. It allows us to see a wide array of colors and light,, but it's inferior to that of other creatures, who can often see light at infrared, ultraviolet and x-ray wavelengths. We, on the other hand, are constrained to only being able to see light in a narrow portion of the electromagnetic spectrum (in visible light). At least, that's what we thought. In a recent twist, new research seems to suggest that, under a certain set of conditions, the human retina can pick up light that's typically invisible to us. 

The research — spearheaded by scientists from the Washington University School of Medicine — centers on powerful lasers, and retina cells collected from both humans and mice. The team used lasers that steadily emit pulses of infrared light, and when these rapid pulsations were exposed to the retina cells, they learned that light-sensing cells sometimes receive a "double hit of infrared radiation," which is a revelation in and of itself.

"They were able to see the laser light, which was outside of the normal visible range, and we really wanted to figure out how they were able to sense light that was supposed to be invisible," explained Frans Vinberg, one of the study's co-authors.

Image Credit: Christian G./Flickr

For some insight, Vinberg, Kefalov and other members of the research team looked to credible scientific literature, specifically focusing on people who claimed to have seen light at infrared wavelengths before. Naturally, most of these reports were brushed off, but they needed a larger pool of information to draw from. Picking out the most credible, and easily replicable mentions, the team recreated the laser experiments to not only see whether it is indeed possible to see infrared light, but to pinpoint the exact manner in which the human eye can pick it up at all. 

"We experimented with laser pulses of different durations that delivered the same total number of photons, and we found that the shorter the pulse, the more likely it was a person could see it," one co-author explained. "Although the length of time between pulses was so short that it couldn't be noticed by the naked eye, the existence of those pulses was very important in allowing people to see this invisible light."

The explain further: 

"We're using what we learned in these experiments to try to develop a new tool that would allow physicians to not only examine the eye but also to stimulate specific parts of the retina to determine whether it's functioning properly," said senior investigator Vladimir J. Kefalov, PhD, associate professor of ophthalmology and visual sciences at Washington University. "We hope that ultimately this discovery will have some very practical applications."

Also noted in the press release: 

The findings were published on December 1st in the Proceedings of the National Academy of Sciences (PNAS). See the full press release here

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